CI: test on Node 16, switch to newer cimg images (#5137)

Node 16.0.0 is now released; we should run CI against it.

The older circleci/node Docker images we use in the Apollo OSS orb do not yet
have 16.0.0. It seems reasonable to switch over to the "non legacy" cimg/node
Docker images anyway. Those images don't have "major version" tags like 16, just
tags like 16.0.0 and 16.0.  So let's switch over to specifying images directly
in config.yml rather than via our orb, and let Renovate update it. See
https://github.com/renovatebot/renovate/blob/92aab2b30f5c0d811056a1574354e97057c42732/lib/manager/circleci/extract.ts#L49
for what Renovate is looking for.

This PR does not convert to using npm v7 (and its new package-lock.json format);
we should do that soon.

.circleci/config.yml

@@ -38,7 +38,8 @@ jobs:
   # at https://hub.docker.com/r/circleci/node/.
 
   NodeJS 12:
-    executor: { name: oss/node, tag: '12' }
+    docker:
+    - image: cimg/node:12.22.1
     steps:
       - common_test_steps
       # We will save the results of this one particular invocation to use in
@@ -52,7 +53,14 @@ jobs:
             - ./**
 
   NodeJS 14:
-    executor: { name: oss/node, tag: '14' }
+    docker:
+    - image: cimg/node:14.16.1
+    steps:
+      - common_test_steps
+
+  NodeJS 16:
+    docker:
+    - image: cimg/node:16.0.0
     steps:
       - common_test_steps
 
@@ -104,19 +112,23 @@ workflows:
           <<: *common_non_publish_filters
       - NodeJS 14:
           <<: *common_non_publish_filters
+      - NodeJS 16:
+          <<: *common_non_publish_filters
       - "Check for FIXM\x45"
       - oss/lerna_tarballs:
           name: Package tarballs
           <<: *common_non_publish_filters
           requires:
             - NodeJS 12
             - NodeJS 14
+            - NodeJS 16
       - oss/dry_run:
           name: Dry-run
           <<: *common_publish_filters
           requires:
             - NodeJS 12
             - NodeJS 14
+            - NodeJS 16
       - oss/confirmation:
           name: Confirmation
           type: approval

docs/package.json

@@ -1,6 +1,6 @@
 {
   "engines": {
-    "node": ">=14 <15",
+    "node": ">=16 <17",
     "npm": "6.x"
   },
   "scripts": {

package.json

@@ -21,7 +21,7 @@
     "coverage:upload": "codecov"
   },
   "engines": {
-    "node": ">=14.0 <15.0",
+    "node": ">=12",
     "npm": "^6.14.11"
   },
   "dependencies": {